:root {
  --bg-color: #f0f2f5;
  --win-gray: #c0c0c0;
  --win-border-light: #ffffff;
  --win-border-dark: #7b7b7b;
  --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  user-select: none;
  -webkit-user-select: none;
}

body {
  background-color: var(--bg-color);
  font-family: var(--font-family);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 16px;
}

.container {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  max-width: 480px;
  width: 100%;
}

header {
  width: 100%;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.back-link {
  color: #333;
  text-decoration: none;
  font-weight: 700;
  font-size: 0.95rem;
}

h1 {
  font-size: 1.6rem;
  color: #222;
}

.difficulty-select {
  display: flex;
  gap: 8px;
}

.diff-btn {
  padding: 6px 14px;
  background-color: #e2e8f0;
  border: 1px solid #cbd5e1;
  border-radius: 6px;
  font-weight: 600;
  font-size: 0.85rem;
  cursor: pointer;
  transition: all 0.2s;
}

.diff-btn.active {
  background-color: #3b82f6;
  color: #fff;
  border-color: #3b82f6;
}

.game-wrapper {
  background-color: var(--win-gray);
  border: 4px solid;
  border-color: var(--win-border-light) var(--win-border-dark) var(--win-border-dark) var(--win-border-light);
  padding: 10px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.15);
}

.control-panel {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background-color: var(--win-gray);
  border: 3px solid;
  border-color: var(--win-border-dark) var(--win-border-light) var(--win-border-light) var(--win-border-dark);
  padding: 6px 10px;
}

.digital-box {
  background-color: #000;
  color: #ff0000;
  font-family: 'Courier New', Courier, monospace;
  font-size: 1.8rem;
  font-weight: 900;
  padding: 2px 8px;
  letter-spacing: 2px;
  border-radius: 2px;
}

.face-btn {
  font-size: 1.8rem;
  width: 44px;
  height: 44px;
  border: 3px solid;
  border-color: var(--win-border-light) var(--win-border-dark) var(--win-border-dark) var(--win-border-light);
  background-color: var(--win-gray);
  cursor: pointer;
  display: flex;
  justify-content: center;
  align-items: center;
}

.face-btn:active {
  border-color: var(--win-border-dark) var(--win-border-light) var(--win-border-light) var(--win-border-dark);
}

.mode-toggle {
  display: flex;
  justify-content: center;
}

.tool-btn {
  padding: 6px 16px;
  border-radius: 4px;
  border: 2px solid #94a3b8;
  background-color: #f8fafc;
  cursor: pointer;
  font-weight: 700;
  font-size: 0.85rem;
}

.board-wrapper {
  overflow-x: auto;
  padding: 2px;
}

.board {
  display: grid;
  border: 3px solid;
  border-color: var(--win-border-dark) var(--win-border-light) var(--win-border-light) var(--win-border-dark);
  margin: 0 auto;
}

.tile {
  width: 32px;
  height: 32px;
  background-color: var(--win-gray);
  border: 3px solid;
  border-color: var(--win-border-light) var(--win-border-dark) var(--win-border-dark) var(--win-border-light);
  display: flex;
  justify-content: center;
  align-items: center;
  font-weight: 900;
  font-size: 1.1rem;
  cursor: pointer;
}

.tile.revealed {
  border: 1px solid #7b7b7b;
  background-color: #d1d5db;
}

.tile.mine {
  background-color: #ef4444;
}

.tile[data-n="1"] { color: #0000ff; }
.tile[data-n="2"] { color: #008000; }
.tile[data-n="3"] { color: #ff0000; }
.tile[data-n="4"] { color: #000080; }
.tile[data-n="5"] { color: #800000; }
.tile[data-n="6"] { color: #008080; }
.tile[data-n="7"] { color: #000000; }
.tile[data-n="8"] { color: #808080; }